Droplet activation behaviour of atmospheric black carbon particles in fog as a function of their size and mixing state

Among the variety of particle types present in the atmosphere, black carbon (BC), emitted by combustion processes, is uniquely associated with harmful effects to the human body and substantial radiative forcing of the Earth. Pure BC is known to be non-hygroscopic, but its ability to acquire a coating of hygroscopic organic and inorganic material leads to increased diameter and hygroscopicity, facilitating droplet activation. This affects BC radiative forcing through aerosol\u2013cloud interactions (ACIs) and BC life cycle. To gain insights into these processes, we performed a field campaign in winter 2015\u20132016 in a residential area of Zurich which aimed at establishing relations between the size and mixing state of BC particles and their activation to form droplets in fog. This was achieved by operating a CCN counter (CCNC), a scanning mobility particle sizer (SMPS), a single-particle soot photometer (SP2) and an aerosol chemical speciation monitor (ACSM) behind a combination of a total- and an interstitial-aerosol inlet. Our results indicate that in the morning hours of weekdays, the enhanced traffic emissions caused peaks in the number fraction of externally mixed BC particles, which do not act as CCN within the CCNC. The very low effective peak supersaturations (SSpeak) occurring in fog (between approximately 0.03\u2009% and 0.06\u2009% during this campaign) restrict droplet activation to a minor fraction of the aerosol burden (around 0.5\u2009% to 1\u2009% of total particle number concentration between 20 and 593\u2009nm) leading to very selective criteria on diameter and chemical composition. We show that bare BC cores are unable to activate to fog droplets at such low SSpeak, while BC particles surrounded by thick coating have very similar activation behaviour to BC-free particles. Using simplified \u3ba-K\uf6hler theory combined with the ZSR mixing rule assuming spherical core\u2013shell particle geometry constrained with single-particle measurements of respective volumes, we found good agreement between the predicted and the directly observed size- and mixing-state-resolved droplet activation behaviour of BC-containing particles in fog. This successful closure demonstrates the predictability of their droplet activation in fog with a simplified theoretical model only requiring size and mixing state information, which can also be applied in a consistent manner in model simulations.Peer reviewed: YesNRC publication: Ye

Experimental methods in chemical engineering: discrete element method-DEM

The Discrete Element Method (DEM) is a time\u2010driven simulation technique based on a Lagrangian description of particle motion that predicts the flow of granular matter and fine powders in conveying, mixing, drying, and heterogeneous gas\u2010(liquid)\u2010solids reactors. Powders flowing out of bins form bridges, they segregate in suboptimal pharmaceutical V\u2010blenders, and a stream may split into large gulf streams as they enter fluidized bed reactors from standpipes and diplegs. To reduce the uncertainty in scaling up these and other powder process unit operations, researchers apply DEM. It integrates Newton\u2019s second law (acceleration equals the sum of the forces) for each particle and models contact between the particles with springs and dashpots (dampers). It is computationally intensive since it calculates the trajectory of all particles. The availability of open source codes, commercial software, and parallel computer architectures has accelerated its adoption in pharmaceutical, agro\u2010industrial and mineral processes, and geophysics. The accuracy of DEM models depends on how well researchers calibrate the contact model expressions and their parameters: friction coefficients and the coefficient of restitution. Systems exceeding 1\u2009 7\u2009108 particles can require weeks of computational time on large computer clusters. Current research targets non\u2010spherical particle interactions and multiphysics problems including heat transfer, mass transfer, and chemical reactions within the particles. The field has grown to 750 indexed aritcles in WoS in 2017. A bibliographic analysis recognized four research clusters: granular materials, behaviour, particle shape, and deformation; flows, fluidized beds, and computational fluid dynamics; particles, impact, and validation; and granular flow, dynamics, and segregation.Peer reviewed: YesNRC publication: N

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Peer reviewed: NoNRC publication: Ye

Llama\ua0peripheral B-cell populations producing conventional and heavy chain-only IgG subtypes are phenotypically indistinguishable but immunogenetically distinct

Camelid ungulates produce homodimeric heavy chain-only antibodies (HCAbs) in addition to conventional antibodies consisting of paired heavy and light chains. In the llama, HCAbs are made up by at least two subclasses (long-hinge IgG2b and short-hinge IgG2c HCAbs vs. conventional heterotetrameric IgG1s). Here, we generated murine monoclonal antibodies (mAbs) specific for the hinge-CH2 boundary of llama IgG2b (mAb 1C10) and the Fc of llama IgG2c HCAbs (mAb 5E4). Flow cytometric analysis of llama peripheral blood lymphocytes revealed that IgG1+, IgG2b+ and IgG2c+ B cells could be distinguished using mAbs 1C10/5E4 but had equivalent expression of three other cell-surface markers. MiSeq sequencing of the peripheral B cell repertoires of three llamas showed that (i) IgG2b and IgG2c HCAbs were present in similar proportions in the repertoire, (ii) a subset of IgG2b and IgG2c HCAbs, but not IgG1s, entirely lacked a hinge exon and showed direct VHH-CH2 splicing; these \u201chingeless\u201d HCAbs were clonally expanded, somatically mutated and derived from hinged HCAb precursors, (iii) substantial repertoire overlap existed between IgG subclasses, especially between IgG2b and IgG2c HCAbs, (iv) the complementarity-determining region (CDR)-H3 length distributions of IgG2b and IgG2c HCAbs were broader and biased towards longer lengths compared with IgG1s due to increased N-nucleotide addition, (v) IgG2b and IgG2c HCAbs used a more restricted set of IGHV genes compared with IgG1s, and (vi) IgG2b and IgG2c HCAbs had elevated somatic mutations rates of both CDRs and framework regions (FRs) compared with IgG1s, especially of CDR-H1 and FR3. The distinct molecular features of llama IgG1, IgG2b and IgG2c antibodies imply that these subclasses may have divergent immunological functions and suggest that specific mechanisms operate to diversify HCAb repertoires in the absence of a light chain.Peer reviewed: YesNRC publication: Ye

Characterization of black carbon particles generated by a propane-fueled miniature inverted soot generator

The miniature inverted soot generator is a novel soot particle generator, capable of producing black carbon (BC) particles with a wide range of properties. The main advantages of this device are its portability, simplicity, low fuel consumption, and relatively low cost compared to other soot generators. In this study, the performance of the miniature inverted soot generator was evaluated using propane as the fuel over a range of air and fuel flow rates. The stability and repeatability of the soot generator to produce BC particles of controlled size distribution, and number and mass concentration was demonstrated. Furthermore, optical absorption, single scattering albedo (SSA), and elemental carbon (EC) and organic carbon (OC) concentrations of the generated particles were measured. When fueled with propane, the miniature inverted soot generator was capable of repeatedly generating particles with average mode mobility diameter ranging from 140\u202fnm to 200\u202fnm, number concentrations 3c4\u202f 7\u202f10\u2076\u2013 3c2.7\u202f 7\u202f10\u2077 #/cm\ub3, and mass concentrations 3c8\u2013 3c140\u202fmg/m\ub3. For many of the investigated operating conditions, the elemental to total carbon ratio (EC/TC) of the generated soot particles was greater than 90%. The mass absorption cross section of generated particles ranged from 3 to 5\u202fm\ub2/g at a wavelength of 870\u202fnm. The results obtained from this study indicate that the miniature inverted soot generator is ideal for producing BC particles with high EC fraction, which can be used as calibration aerosol for BC diagnostic instruments.Peer reviewed: YesNRC publication: Ye

Characterizing the properties of nearby molecular filaments observed with Herschel

Context. Molecular filaments have received special attention recently thanks to new observational results on their properties. In particular, our early analysis of filament properties from Herschel imaging data in three nearby molecular clouds revealed a narrow distribution of median inner widths centered at a characteristic value of about 0.1 pc. Aims. Here, we extend and complement our initial study with a detailed analysis of the filamentary structures identified with Herschel in eight nearby molecular clouds (at distances <500 pc). Our main goal is to establish statistical distributions of median properties averaged along the filament crests and to compare the results with our earlier work based on a smaller number of filaments. Aims. We use the column density (NH2) maps derived from Herschel data and the DisPerSE algorithm to trace a network of individual filaments in each cloud. We analyze the density structure along and across the main filament axes in detail. We build synthetic maps of filamentary clouds to assess the completeness limit of our extracted filament sample and validate our measurements of the filament properties. These tests also help us to select the best choice of parameters to be used for tracing filaments with DisPerSE and fitting their radial column density profiles. Methods. Our analysis yields an extended sample of 1310 filamentary structures and a selected sample of 599 filaments with aspect ratios larger than 3 and column density contrasts larger than 0.3. We show that our selected sample of filaments is more than 95% complete for column density contrasts larger than 1, with only ~ 5% spurious detections. On average, more than 15% of the total gas mass in the clouds, and more than 80% of the dense gas mass (at NH2 > 7 7 10 21 cm -2 ), is found to be in the form of filaments. Analysis of the radial column density profiles of the 599 filaments in the selected sample indicates a narrow distribution of crest-averaged inner widths, with a median value of 0.10 pc and an interquartile range of 0.07 pc. In contrast, the extracted filaments span wide ranges in length, central column density, column density contrast, and mass per unit length. The characteristic filament width is well resolved by Herschel observations, and a median value of ~0.1 pc is consistently found using three distinct estimates based on (1) a direct measurement of the width at half power after background subtraction, as well as (2) Gaussian and (3) Plummer fits. The existence of a characteristic filament width is further supported by the presence of a tight correlation between mass per unit length and central column density for the observed filaments. Results. Our detailed analysis of a large filament sample confirms our earlier result that nearby molecular filaments share a common mean inner width of ~0.1 pc, with typical variations along and on either side of the filament crests of about \ub1 0.06 pc around the mean value. This observational result sets strong constraints on possible models for the formation and evolution of filaments in molecular clouds. It also provides important hints on the initial conditions of star formation.Peer reviewed: YesNRC publication: Ye

Modeling and mapping dynamic vulnerability to better assess WUI evacuation performance

Wildland\u2010urban interface (WUI) fire incidents are likely to become more severe and will affect more and more people. Given their scale and complexity, WUI incidents require a multidomain approach to assess their impact and the effectiveness of any mitigation efforts. The authors recently produced a specification for a simulation framework that quantifies evacuation performance during WUI incidents including inputs from three core domains: fire development, pedestrian performance and vehicular traffic [26]. This framework could produce new insights by simulating evolving conditions of WUI incidents based on developments and interactions between the core components. Thus, it aims to overcome known limitations of previous approaches (eg, static assessment, single domain approaches, or lack of projection), as well as to provide explanatory insights into the outcomes produced by the simulation. The proposed framework would also advance geo\u2010spatial mapping of WUI incidents. The concept of dynamic vulnerability, urn:x-wiley:03080501:media:fam2708:fam2708-math-0001, is at the core of the framework and is enabled by the integrated simulation framework and the emergent conditions predicted. This allows users to construct richer incident narratives from the perspective of specific locations or subpopulations, and also makes fewer simplifying assumptions regarding interactions between the three core domains.Peer reviewed: YesNRC publication: Ye

Candidate list maintenance in high utility sequential pattern mining

High utility sequential pattern mining (HUSPM) lends the aspect of item value or importance to sequential pattern mining by identifying patterns that comprise a significant level of utility in a database. This paper addresses the challenge of establishing upper bounds on future candidate pattern utilities in an effort to reduce the search space required to identify the full set of patterns, and proposes a new approach where a list of possible candidate concatenation items is maintained. This list specifies the only items that ever need to be considered as possible candidates for concatenation with a sequential pattern being considered, or any future sequential pattern appearing as a descendant in the search tree. As a result of the elimination of items that are known to have no possibility of appearing in future high utility sequential patterns, an approach is presented that exploits this knowledge and computes a significantly tighter upper bound on the utilities of the such patterns. Tests on a variety of publicly available datasets show a dramatic reduction in the number of candidates considered, and the time taken to identify the full set of high utility sequential patterns is significantly reduced accordingly.Peer reviewed: YesNRC publication: Ye

A probabilistic high-pressure zone model for local and global loads during ice-structure interactions

For temperate ice regions, guidance provided by current design codes regarding ice load estimation for thin ice is unclear, particularly for local pressure estimation. This is in part due to the broader issue of having different recommended approaches for estimating local, global, and dynamic ice loads during level ice interactions with a given structure based on region, scenario type, and a variety of other conditions. It is essential from a design perspective that these three scenarios each be evaluated using appropriate definitions for local design areas, global interaction area, and other structural details. However, the need for use of different modeling approaches for ice loads associated with each of these scenarios is not based on ice mechanics but rather has largely evolved as a result of complexities in developing physics-based models of ice failure in combination with the need to achieve safe designs in the face of limited full-scale data and the need for implementation in a probabilistic framework that can be used for risk-based design assessments. During a given interaction, the ice is the same regardless of the design task at hand. In this paper, a new approach is proposed based on a probabilistic framework for modeling loads from individual high-pressure zones acting on local and global areas. The analysis presented herein considers the case of thin, first-year sea ice interacting with a bottom-founded structure based on an empirical high-pressure zone model derived from field measurements. Initial results indicate that this approach is promising for modeling local and global pressures.Peer reviewed: YesNRC publication: Ye

Bell 412 system identification: comparing methods and tools

Over the last decades system identification has become a standard method for developing rotorcraft models from flight test data. Using data from the Bell 412 Advanced Systems Research Aircraft (ASRA) helicopter operated by the National Research Council of Canada, different identification methods and tools are applied to a common database. The identified 6-DoF rigid-body models at one flight condition are compared in detail regarding eigenvalues and the match in both time and frequency domain. The development of a global model from point models that were identified at the different flight conditions is described. Finally, several possible extensions of the rigid-body models are investigated assessing corresponding improvement in model fidelity.Peer reviewed: NoNRC publication: Ye